This invention relates to a transparent conductive multi layer film excellent in antistatic effect, electromagnetic wave shielding, antireflection, mechanical strength and anti-smudge. More particularly it relates to a transparent conductive film useful for antireflection of the face panel (i.e., the front panel) of cathode-ray tubes, plasma displays, etc.
A transparent antistatic and electromagnetic wave shielding material has been demanded for various electronic equipment. For example, a cathode-ray tube or a plasma display used in TV sets or computer displays easily attracts dust by static electrification of the front panel to reduce visibility or radiates electromagnetic waves to give adverse influences to the surroundings. An antireflection function has also become necessary to cope with the tendency of the cathode-ray tube flattening. Additionally the front panel is liable to receive scratches by the touch with fingers or on cleaning.
For the purpose of statiec prevention, electromagnetic wave shielding and antireflection, it has been proposed to form a conductive layer comprising a metal such as silver or a conductive metal oxide such as indium-tin oxide (ITO) directly on the front panel by vapor deposition or sputtering technique. However, such vapor deposition and sputtering techniques involve a vacuum treatment or a high temperature treatment, which increases the production cost, or have poor productivity.
Thin conductive film formation techniques based on a sol-gel process have also been proposed [see Habu et al., National Technical Report, Vol. 40, No. 1, p. 90 (1994) and Y. Ono et al., SID 92DIGEST, 511 (1992)]. However, these techniques also require a high temperature treatment. Besides, film formation on a transparent substrate, i.e., a plastic film or a hard coat, tends to induce denaturation of the substrate, which has limited the choice of the substrate material.
Transparent conductive coatings having dispersed therein conductive oxide particles or colloidal particles have also been proposed [see JP-A-6-344489 and JP-A-7-268251 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and H. Murakami et al., SID 89 DIGEST, 270 and SID 93 DIGEST, 209, (1998)]; but the resulting transparent conductive layer has insufficient conductivity.
In order to improve conductivity of the conductive films, JP-A-9-55175 proposes a transparent conductive film obtained by applying a coating composition comprising metal particles. JP-A-10-142401 discloses a low-reflection transparent conductive film obtained by applying an antireflective coating composition comprising tetraethoxysilane, etc. on a transparent conductive film. However, the film formed by merely coating a transparent substrate with metal particles has insufficient mechanical strength, and the antireflective coating such as tetraethoxysilane should be treated in high temperature for a long time. Since formation of an antireflective layer by a sol-gel process limits the material of the transparent substrate, the above-mentioned low-reflection transparent conductive film cannot be carried out except by directly applying the coating composition to the glass face panel.
Instead of the method comprising direct application of a coating composition to a face panel which entails high initial cost and requires a high temperature treatment, methods of attaching a thin film formed on a separate substrate to the face panel have been developed (see Taki et al., National Technical Report, Vol. 42, No. 3, pp. 264-268 (1996)). These methods rely on thin film deposition techniques in a vacuum system, such as vacuum evaporation, sputtering and the like for forming a conductive metal oxide film (e.g., ITO), which are very costly and less productive as previously mentioned.
On the other hand, it is necessary to ground a conductive layer for electromagnetic wave shielding as described in JP-A-10-3868. Where the conductive layer has a protective layer, it is difficult to lead a grounding wire from the protective layer. In order to be grounded, the conductive layer should be provided with some grounding terminals or be partially exposed by some means. For example, grounding of the conductive layer has been carried out by adhering a conductive tape to the conductive layer before formation of a low-refractive layer thereon, or partly peeling the surface protective layer, or piercing the protective layer, or ultrasonic welding. Such a processing step for grounding is very likely to be accompanied by damages such as scratches to the conductive layer, the protective layer or any other functional layers, resulting in deterioration of weather resistance and impairment of the commercial value. These extra steps also contribute to an increase of cost and a reduction of productivity.
An object of the present invention is to provide a low-reflection conductive multi layer film which is excellent in productivity as well as antistatic properties, electromagnetic wave shielding performance, reflection preventive properties, mechanical characteristics and anti-smudge properties and which can be stuck to a face panel (i.e., a front panel).
Another object of the invention is to provide a transparent conductive film which is excellent in productivity in directly grounding the surface of the conductive film.
The above objects are accomplished by a low-reflection transparent conductive multi layer film comprising, in the order described, a transparent substrate, a hard coat, a transparent conductive layer containing particles comprising at least one of a metal and a metal oxide, and at least one transparent protective layer for the conductive layer which has anti-smudge properties and has a refractive index different from that of the transparent conductive layer.
The low-reflection transparent conductive film of the invention is directly attached to a cathode-ray tube or a plasma display panel used in a TV set or a computer display to perform the desired functions with greatly simplified equipment through greatly simplified steps as compared with the conventional vapor deposition techniques such as PVD or CVD or the conventional method comprising applying a conductive coating directly to the face panel. The invention also allows the surface of the protective layer to be grounded directly, which leads to simplification of the production steps.